Precision Targeting of Breast Cancer Cells by Placental Homing Peptides: A Novel Approach for Improved Drug Delivery

Abstract

Breast cancer is a significant cause for concern internationally owing to its high incidence and mortality rates. The five-year survival rate for metastatic breast cancer, even with adjuvant treatment, is low. Despite the availability of conventional therapies, there is a need for the development of new drug formulations that can effectively mitigate the overall toxicity associated with existing medications, while simultaneously enhancing their selectivity and efficacy. Homing peptides have been successfully utilised as therapeutic targeting agents for cancer therapy. Nanoparticles decorated with tumour-homing peptides have proven to enhance treatment effectiveness by selectively delivering chemotherapeutics directly to their sites of action. Tumour homing peptides have also been found to home to placental tissues, hence providing the first options to target the delivery of therapeutic agents to the placenta. The aim of this work is to evaluate the reciprocal possibility, that placental homing peptides could be used for targeted drug delivery in breast cancer treatment. In the present work, the binding affinity of the placental homing peptides NKG (NKGLRNK) and RSG (RSGVAKS) to breast cancer cells grown in 2D conditions is first demonstrated using fluorescence microscopy and flow cytometry techniques. Then for the first time, the ability of two novel placental homing peptides, NKG and RSG, to deliver liposomally-encapsulated doxorubicin (DOX) to breast cancer cells when cultured in either 2D conditions or 3D alginate-gelatin hydrogels, to represent tumour extracellular matrix (ECM) of differing stiffnesses, is evaluated. Then, on the basis that the lipid composition of cell membranes affects homing peptide binding and internalisation, a systematic translational characterisation is performed using reflectometry techniques with model cancer and placental membranes that mimic the primary lipid compositions of the respective cells to reveal the extents of interactions of RSG and the tumour homing peptide CGKRK. NKG- and RSG-decorated liposomes facilitate equivalent delivery of DOX to MDA-MB-231 and MCF-7 cells and exhibit comparable cytotoxicity to those decorated with the well-characterised tumour homing peptide CGKRK, in both 2D and 3D systems. ECM stiffness-dependent resistance to treatment with free DOX and peptide-decorated DOX-loaded liposomes is revealed, consistent with the resistance of some later-stage human tumours to treatment, suggesting that our liposomal formulation may be most effective in early-stage breast cancer. Model lipid membrane studies have demonstrated that RSG exhibits stronger interactions and greater penetration than CGKRK into both model membrane types, combined with greater disruption of the lipid component, which is attributed to its greater hydrophobicity. These findings suggest that NKG and RSG represent novel tumour-binding sequences that exhibit potential for exploitation in the development of new, effective therapeutic agents for targeted breast cancer therapy. More generally, this work has developed and validated a new platform for gaining novel insights into key processes that govern membrane interactions of homing peptides, which will aid the design of more efficacious targeted drug delivery agents.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Richard Campbell (Supervisor) & Harmesh Aojula (Supervisor)